VMware/VCP5 Prep Series: Creating and Configuring VMware Clusters

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In this article we will learn how to create and configure a VMware vSphere cluster using a Web Client.

A cluster is a group of ESXi hosts added together to provide compute, storage and network capacity to virtual machines running in the ESXi which is part of the cluster. It is administered by a vCenter server collectively and creating a cluster enables the hosts to work together so that they provide a higher level of availability to virtual machines than each ESXi host could provide individually.

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When you create a vSphere HA cluster, the HA elects a single host as the “Master Host” while the rest of the nodes become slave hosts. The master host communicates with the vCenter server and monitors the state of other hosts and protected virtual machines of the cluster. Different types of host related issues are possible and the master host is responsible for detecting and dealing with these issues appropriately.

Figure 1: Image Courtesy of VMware

The master host can deduct host failures or isolation by monitoring the network heartbeat from each ESXi host every second.

Figure 2: Image Courtesy of VMware

If the master host does not receive a heartbeat, it determines if the slave host is heart beating to one of the cluster’s datastore. If both fail, the slave host is considered to have failed and the HA will restart the failed host virtual machine on an alternate ESXi host.

Figure 3: Image Courtesy of VMware

If the host is still heart beating with the datastore, then it might only be network isolated. This means that the host is still running but it cannot observe the vSphere HA management network. In this case, the master host continues to monitor the host and if the virtual machine powers off, the master host restarts the VM on another host in the cluster.

Now let’s learn how to create a VMware HA Cluster using a Web Client.

1. Login to the web client, select Home screen and then “Hosts and Clusters.”

4. In DRS, “Migration Threshold” is set at value 3 by default and automation level will be “fully automated.” Change these settings as per the requirement; there are 3 types of automation levels available in DRS.
4.1 Manual – The vCenter server will only suggest migration recommendation for virtual machines, so the VMs need to be manually set to vMotion across the ESXi hosts.
4.2 Partially Automated – The virtual machine will be automatically placed on the host at power on and vCenter will suggest migration recommendations for virtual machines.
4.3 Fully Automated – The virtual machine will be automatically placed on the host at power on and will be automatically migrated. DRS will decide which host to place Virtual Machines on at start up, and to vMotion Virtual Machines to other hosts based on resource utilization.

HA (High Availability) When “vSphere HA” is enabled, host monitoring is enabled by default. This will enable the host to exchange heartbeat between them as discussed earlier. This is key for the functionally of the HA cluster.

Next is “Admission Control.” The vCenter Server uses admission control to ensure that sufficient resources are available in a cluster to provide failover protection and to ensure that virtual machine resource reservations are respected. Two types of admission control are available in this screen.

Hosts Failures the cluster tolerates: Specified in the number of hosts

5. Choose whether to enable VM Monitoring (requires VMware Tools to be installed). Use the slider to choose the Monitoring Sensitivity.

6. By default, EVC is set to disabled, so set to enabled if required. This ensures that all hosts in a cluster present the same CPU features set to virtual machines, even if the actual CPUs on the hosts differ. This prevents migrations with vMotion from failing due to incompatible CPUs.

7. The last option is VSAN. Turn it on if required and by default “Add disk to storage” is set to automatic. Click on the “OK” button to complete the cluster configuration.

8. Select the Cluster and chose the “Manage” tab, then select vSphere HA and click on the Edit button.

9. Under “Admission Control” we have more options presented compared to when we created the HA Cluster. In this screen we have the option to specify a “Fixed slot size” for CPU and Memory. Also, there is an additional option to calculate VMs that require multiple slots.

10. An additional option is available to dedicate specific ESXi hosts as failover hosts.

12. The next option is Datastore Heart beating: the master host uses the datastore heart beating as the second measure to check if the host is isolated before declaring it is failed and restarts the VMs on the failed ESXi host. Three options are available. After completing this step, the cluster configuration is complete and we can start adding an ESXi host to facilitate compute, network and disk requirements to the virtual servers.

Now that we have our HA/DRS cluster up and running, the next task is to add an ESXi host on to the cluster. The steps below will easily get the host added to the cluster.

1. Right click on the Cluster and select “Add Host.”

2. In the Add host wizard type, enter the host name or IP address of the host that needs to be added to the cluster.

3. In the “Connections Settings” screen, key in the root credentials for the ESXi host and click next.

4. The wizard will provide an ESXi host summary, including the build version and a list of VMs registered on this host. Click next.
5. License the ESXi host. In the next screen, leave “Enable lockdown mode” unchecked. When enabled, lockdown mode prevents remote users from logging directly into this host.
6. In the resource pool screen, you can either leave it in default, which is “root” resource pool, or create a new resource pool based on the requirement. Then click next.

7. The final step provides a summary of all the options we selected. Click the finish button. The ESXi host will be added to the HA/DRS Cluster.

Summary

In this article, we learned the steps involved in creating a HA and DRS cluster. We discussed the additional configurations required after creating the cluster, such as Admission Control, VM monitoring and Datastore heart beating.

It is crucial for vSphere administrators to understand the functionalities of a VMware cluster. Creating a cluster is a straightforward process, but proper consideration must be utilized in the configuration for the cluster to function optimally.

I hope you enjoyed this topic on VCP5 preparation and thank you for reading!

Ravi Kumar (@ravi_kummar) - VCAP5-DCA, VCP-DCV 4, 5, VCA5-Cloud, VCA5-DCV. He has been working with VMware's technologies for almost 7 years, he has worked in various fields, from consulting, support, to training. Ravi blogs regularly in his personal blog (http://raviitblog.com). He has been recognized as vExpert 2014 for his contributions to the community.

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